The aim of the proposed research is the isolation of the actin genes from Drosophila melanogaster DNA using the heterologous probe, actin mRNA from Dictyostelium discoideum. Because of the evolutionary conservation of the actin protein, it is expected that the nucleotide sequence encoding the protein will also be conserved among species. Partially purified Dictyostelium actin mRNA will be used to select recombinant Drosophila DNA fragments which will be characterized with regard to their organization within the genome, transcriptional activity and replication. Since current evidence indicates that multiple genes are present in Drosophila, regulation of the genes during development can be studied. Transcriptional activity will be studied using in situ hybridization of DNA to nascent RNA in polytene chromosomes of tissues at different stages of development. DNA sequences adjacent to the 5' ends of the mRNA coding region will be examined for putative control regions. The intent of this research is to study control of gene regulation and constancy of sequence organization by examination of a specific set of structural genes. Information regarding eukaryotic gene regulation is of importance in understanding processes occurring during development, and changes in these processes which result in pathological or neoplastic conditions. A second intent is to demonstrate that specific genes can be isolated using partially purified heterologous probes when highly purified homologous probes are not available. Extension of this type of selection to genes coding for other highly conserved proteins such as tubulin is the next feasible step.